The present invention relates to a novel and improved process for the preparation of a polymer membrane which is useful for the selective separation of a liquid mixture Particular, the present invention relates to a process for the preparation of an interpenetrating polymer network membrane composed of hydrophilic-hydrophobic two phase structure with a varying degree of segregation of the hydrophilic and hydrophobic component by a polymerization reaction comprising controlling the relative rate of polymerization of the component polymers, or controlling the reaction temperature and the reaction pressure during the interpenetrating polymer network forming reaction. More particularly, the present invention relates to a process for the preparation of an interpenetrating polymer network (IPN), the (IPN) being a crosslinked polymer alloy, which is utilized for the separation of a liquid mixture, by a simultaneous polymerization and crosslinking reaction or a sequential polymerization and crosslinking reaction, to form a urethane resin of general formula (I) ##STR5## wherein R.sub.1 is ##STR6## wherein R.sub.3 stands for hydrogen or methyl group, n is integer of 1-3 and m is integer of 5-40,
R.sub.2 is either ##STR7## wherein n is integer of 2-8, and a styrene resin of general formula (II) ##STR8## wherein R.sub.4 is hydrogen or methyl group.
For the separation of liquid mixtures, heretofore, conventional distillation techniques were mostly ulilized. However, these techniques are not suitable for the separation of components with close boiling point ranges, azeotropic mixtures and heat-sensitive mixtures. Consequently, separation techniques utilizing polymer members which are both, energy conserving and simple in operation are, under development, (R. E. Kesting, Synthetic Polymeric Membranes, McGraw Hill, New York 1971). A separation memberane is defined as a membrane selectively permeable to a specific component in the mixture, and the general requirement of the membrane is high permeability and good mechanical properties.
When the affinity between the liquid mixture and membrane is high, the swelling of the membrane increases thus enhancing the permeability. However, the increased swelling usually reduces the permselectivity and the mechanical strength property of the membrane. Therefore, a polymer membrane with well balanced permeability, permselectivity and mechanical properties, is desired.